Exploring biological relationships between calving traits in primiparous cattle with a Bayesian recursive model.

Area of Science:

• Animal Genetics
• Reproductive Biology
• Quantitative Genetics

Background:

• Calving difficulty (CD) and stillbirth (SB) significantly impact cattle production.
• Understanding the relationship between gestation length (GL) and calving traits is crucial for improving animal welfare and economic efficiency.

Purpose of the Study:

• To investigate the biological relationships between gestation length (GL), calving difficulty (CD), and stillbirth (SB) in cattle using advanced statistical modeling.
• To identify the optimal gestation length for minimizing calving difficulty and perinatal mortality.

Main Methods:

• Employed recursive structural equation models (SEMs) with heterogeneous structural coefficients.
• Analyzed a large dataset of 90,393 primiparous cows, including records for GL, CD, and SB.
• Utilized a liability threshold model for categorical traits (CD and SB) within an acyclic SEM framework.

Main Results:

• Found low genetic correlations between gestation length (GL) and calving difficulty (CD) or stillbirth (SB).
• Observed high and positive genetic correlations between the liabilities for CD and SB.
• Identified an intermediate optimum for GL, with gestations around 274 days (3 days shorter than average) associated with the lowest CD and SB.

Conclusions:

• Gestation length has a complex, non-linear relationship with calving difficulty and stillbirth in cattle.
• Targeting an intermediate gestation length, specifically around 274 days, can effectively reduce calving complications and perinatal mortality.
• The genetic liability for calving difficulty and stillbirth is strongly interconnected.